In high current voltage regulators used in laptop, desktop, server and telecom applications, adaptive voltage position (AVP) control is widely used to achieve good transient performance and reduce load power consumption. FIG. 1A illustrates the basic principle of AVP control, wherein Vout represents an output voltage of a voltage regulator, Iout represents an output current of the voltage regulator and Vref represents a reference voltage. As shown in FIG. 1A, output voltage Vout linearly decreases within a voltage tolerance window (Vmax−Vmin) as output current Iout increases, where Vmax is a permitted maximum output voltage, and Vmin is a permitted minimum output voltage.
FIG. 1B compares load transient response of voltage regulators with and without AVP control. As shown in the figure, for voltage regulators without AVP control, because of undershoot and overshoot at the output voltage Vout during load transient period, only half of the voltage tolerance window can be used. While in voltage regulators with AVP control, output voltage Vout is controlled to be slightly higher than permitted minimum output voltage Vmin at full load, and a little bit lower than permitted maximum output voltage Vmax at light load. As a result, the entire voltage tolerance window can be used during load transient period, which allows a smaller output capacitor in the voltage regulator. Furthermore, since output voltage Vout with AVP control decreases as the output current Iout increases, the output power at full load is degraded, which greatly facilitates the thermal design.
However, with fast development of electronic devices, higher and higher power is pushed on voltage regulators. The traditional AVP control may be not enough to achieve both fast transient response and safety operation within the voltage tolerance window.